This invention relates to a process for the roller-application of an aqueous thixotropic coating composition to a surface at ambient temperatures, say 5 to 35.degree. C. The invention also relates to a combination for use in the process. The process and combination are most suitable for use with coating compositions such as paints, distempers, varnishes or woodstains which are conventionally applied to surfaces found on buildings. The process and combination are both easy to use by unskilled amateur or "Do-it-Yourself" (i.e. "DIY") painters, in that they substantially reduce and usually, almost eliminate mess from rollers, provided that they are used with a reasonable degree of common sense. The process and combination also reduce the amount of physical effort involved in painting, so making it a less tiring activity, especially for unskilled amateurs.
Roller-mess can occur in three ways. Firstly, the painter may load too much paint onto the roller so that it drips as it is being taken from a container of paint to the surface to be painted. Secondly, because rollers rotate during the application of the paint to a surface, blobs of overloaded paint are caused to fly off the roller by the centrifugal force they experience. This is known as "fly-off" in the British trade. Thirdly, probably all aqueous paints used in painting buildings at ambient temperatures contain cellulosic or similarly elastic thickeners. Such thickeners cause the paint to break up into droplets in the space just behind the roller causing a fine spray of paint known as "roller-spatter". Roller-spatter is described by R H Fernando et al in the book "Polymers in Aqueous Media", edited by J E Glass and published by the American Chemical Society of Washington in 1989 (see pages 247 and 248 and especially the photograph on page 248).
An early attempt to minimise mess from contact-coating tools (for example rollers, brushes or pads) was disclosed by Berger, Jenson & Nicholson Limited in British Patent Specification GB 922 456 published in 1963. GB 922 456 discloses the addition of titanium chelates to aqueous paint formulations containing cellulose. The chelate creates a gel structure which inhibits dripping, yet which breaks down under the shear forces experienced during application of the paint to the surface, with the result that the production of smooth coatings is still possible. The use of titanium chelates was and still is a major commercial success in the field of brush-painting, but it has been found to aggravate the problem of fly-off during roller-painting. This is because the gelled structure enables even bigger blobs of paint to be picked up by a contact-coating tool, which means that even more paint is available to fly when the tool is one which rotates, i.e. a roller.
The next commercially successful development relating to mess-free painting related specifically to roller-painting and it was disclosed by one of the present Applicants in their European Patent Specification EP 0 144 135A published in 1985. EP 0 144 135A disclosed the addition of large amounts of titanium chelate (or equivalents such as zirconium chelate or gel-forming clays) to aqueous paint formulations containing cellulosic thickeners, so producing a paint so highly gelled that it was virtually solid. The solid paint was formed in a tray dimensioned so as to be able to receive a roller of standard size and the roller was loaded by pressing it against the surface of the paint and rolling it back and forth. Such rolling liquefies the top two or three millimeters of the surface of the paint, but only the top two or three millimeters so that the paint is taken up onto the roller in a very regulated way, which significantly reduces the risk of blob-formation. In addition, roller spatter is virtually eliminated possibly because the highly regulated loading ensures a very uniform and light loading of paint, which is then less able to execute extensive elastic deformations.
The concept of a solid paint in a roller-tray was and is a major commercial success in the field of roller-painting in Britain and Germany. However, it has three disadvantages. Firstly, formation of a gel which is virtually solid takes a long time, so the paint has to be stored in its trays for about 4 weeks and this is expensive in terms of warehouse space. Secondly, each tray of paint is heavy and unwieldy to handle, especially when a painter is up a ladder, as when painting a ceiling for example. Thirdly, as paint is applied to the surface being painted, the roller has to be repeatedly returned to the tray for re-loading with a further supply of paint. Re-loading is tiring because it involves pressing the roller against the solid paint and it is time-consuming because several traverses of the roller across the paint surface have to be made. Clearly what is needed is a technique for transferring highly structured paint from a supply container to a roller in a way which is essentially non-tiring, non-time-consuming but highly regulated.
The paint trade has spent most of this century looking for a commercially acceptable way to load rollers or brushes with paint delivered under pressure during painting, so as to avoid the interruptions and fatigue caused by re-loading. For example, as long ago as 1913, United States Patent Specification U.S. Pat. No. 1,065,610 described a "fountain" paint brush incorporating a channel through which paint under pressure could be delivered and loaded onto the bristles of the brush. Similar systems were still being proposed in 1968 (see Belgian Patent Specification BE 672 437), in 1976 (see United States Patent Specification U.S. Pat. No. 3,960,294), in 1980 (See World Patent Specification WO 80/00315), in 1985 (see British Patent Specification GB 2 142 386A) in 1986 (see French Patent Specification FR 2 575 909) and in 1993 (see United States Patent Specification U.S. Pat. No. 5,246,302). So far, no system of this type has achieved significant commercial success, despite the long sustained world-wide interest in trying to solve the problem. For example, a system based on the disclosure of WO 80/00315 was launched commercially in the early 1980's, but a lack of commercial success forced its withdrawal from the market less than two years later.
A recent confidential study of the above failures has led to a new insight into what the systems lacked at least in the eyes of unskilled amateur (i.e. Do-it-Yourself) painters. To succeed, a system must be simple, reasonably inexpensive to manufacture and it must be non-tiring and lightweight so that it can be easily carried (for example on a shoulder strap) during painting by an unskilled (often female) amateur painter. It must be able to deliver pressurised paint at the touch of an easily accessible button or lever and without the need for interruption of the painting operation. The system must also be able to accommodate different paints of alternative colours and/or sheens (i.e. matt, silk or gloss sheens) without the need to clean a paint reservoir. Above all for roller-painting by amateurs, commercial experience with solid paints has shown that avoidance of fly-off and roller-spatter are extremely important advantages relative to more conventional roller-painting systems. In practical terms, this means that the roller must be loaded in a very regulated way which in turn means that the system must be able to deliver paint to the roller in a very steady flow.
The system which is described in principle in WO 80/00315 employed paint provided in a rigid container/reservoir adapted to receive a rupturable capsule of liquefied carbon dioxide. Such a system presents several problems. Firstly, the paint was pressurised by rupturing the capsule to create a high super-atmospheric pressure of carbon dioxide *within the reservoir. Amateur painters have an instinctive fear of such capsules and high super-atmospheric pressures. Secondly, to avoid wasting the carbon dioxide, the container/reservoir had to be capable of making a sustainable efficient gas-tight seal with the rest of the system. In order to guarantee a seal of this quality, the containers had to be quite robust and had to be moulded very accurately under very clean conditions and this added to their weight and cost. Thirdly, the carbon dioxide pressure decreases during use and so likewise the rate at which the paint is forced along the tube from the reservoir to the roller also decreases. This means that a constant rate of loading of the roller cannot be achieved, nor can the change in the rheological properties of the paint due to loading be kept constant.
Alternative pressurising techniques comprising the exertion of super-atmospheric air-pressure on paint contained in a flexible container are disclosed in U.S. Pat. No. 3,960,294 (published in 1976), in GB 2 142 386A (published in 1985) and in U.S. Pat. No. 5,246,302 (published in 1993). None of these publications discloses the importance of creating a steady pressure, so that the change in the rheological structure of the paint as it is forced through a long delivery tube is likewise steady.
Confidential consumer research has shown that, for the system to be attractive to the unskilled amateur painter, it must offer not only non-tiring relatively mess-free roller-painting using paint delivered under pressure, but also the system must
a) be almost as mess-free as roller-painting using solid paint, PA1 b) employ only slightly superatmospheric pressure, PA1 c) employ a light-weight air-compressor powered by a small cheap electric battery and PA1 d) accommodate a delivery tube about 1.3 to 2.3 m long, which can comfortably lead from a flexible bag of paint either supported on the floor or carried by the painter at her waist or on her back. PA1 a) the supply of appropriate paint in a container biased to horizontal compression during use and preferably provided with an internal channel-defining spacer, PA1 b) the compression of the paint container in a horizontal direction preferably accompanied by a downwards force and PA1 c) the choice of the correct range of internal diameters for the long delivery tube. PA1 a) supplying the coating composition in a flexible container having an outlet, PA1 b) compressing the container by means of air pressure to expel the coating composition from the container via the outlet, PA1 c) transferring the expelled composition via a delivery tube 1 to 3 m long onto a roller and PA1 d) transferring the composition from the roller onto the surface characterised in that the process also includes PA1 e) biasing the container to be compressible in a horizontal direction during use by the provision of opposed flexible walls spaced apart by a flexible transverse base having a flexible crease which extends between the walls, PA1 f) using an air-pressure of from 1.8 to 2.3 bar absolute to inflate a flexible bag and urge it horizontally against one of the opposed walls of the container to cause the compression which expels the coating composition and PA1 g) subjecting the coating composition to the effects of passage through a 1 to 3 m long tube of internal diameter 5 to 15 mm. PA1 a) a housing for parts of the combination, the housing including opposed walls, PA1 b) coating composition supplied in a flexible container having an outlet and located within the housing, PA1 c) means for compressing the container by use of air pressure so as to expel coating composition from the container via the outlet and PA1 d) a delivery tube 1 to 3 m long, one end of which communicates with the outlet from the container and the other end of which is connectable to a roller adapted to receive a delivery of the composition under pressure characterised in that PA1 e) the container includes PA1 f) the means for compressing the container includes a flexible inflatable bag located adjacent one of the opposable walls of the container and adjacent one of the walls of the housing whereby expansion of the bag by an air-pressure of from 1.8 to 2.3 bar urges the bag against the walls to cause horizontal compression of the container and PA1 g) the delivery tube has an internal diameter of 5 to 15 mm. The above described process and combination can also be used in applying coating using a brush or a pad, rather than a roller applicator. PA1 i) a fixed shear-rate viscosity of from 0.06 to 0.25 pa.sec (0.6 to 2.5 poise) when measured at a shear-rate of 10,000/sec, PA1 ii) a fixed shear-stress viscosity of from 0.8 to 3.0 pa.sec (8 to 30 poise) when measured at a shear stress of 120 Pascal (1,200 dyne/cm.sup.2) and PA1 iii) a Rotothinner mid-shear viscosity of from 0.5 to 5.0 pa.sec (5 to 50 poise),
It has now been discovered that these requirements can be met by a combination of
More specifically, it has been found that a reliably steady delivery of appropriate paint to the roller can be achieved using an air pressure of only 1.8 to 2.3 bar which is easily obtained using an air compressor powered by no more than a 3.5 volt electric battery of 0.7 to 2 amp hour size and which can be sustained for up to 10 hours.